How do I change the properties for more than one activity at a time?
Multiple activities, and even multiple objects, may be modified simultaneously. First, select the desired objects on the canvas by drawing a box around them with the Select Tool or by selecting them individually with the Multi-Select Tool. Next, click Object Properties > Set Properties for Selected Objects… from the menu bar.
Each tab of the corresponding window contains any properties which may be modified globally. Notable exclusions include unique properties, such as descriptions and IDs. Any change made will override the individual settings for all objects selected, but only for the given type. For example, if the box next to float is checked in the Activity tab, every activity selected will have its float displayed on the canvas, but not every milestone. The box next to float would have to be checked in the Milestone tab as well.